Profitable Wonders
James Le Fanu
‘All nature is at war, one organism with another,’ wrote Charles Darwin.
One might suppose the constant danger for most creatures of being eaten by those higher up the food chain must make life a fearful business.
In fact, the general impression, for even the most vulnerable, is of a harmonious, almost carefree existence, secure in possessing some useful protective trait against being caught and killed.
There is security in being difficult to see. Hence the resemblance, for the purposes of camouflage, of animals’ colouring to their surroundings: brownish for the inhabitants of the Sahara desert; brilliant green for the tree-dwellers of the Amazonian forest.
Or, better still, the invisibility conferred by the mimicry so prevalent in insects disguised as inedible sticks, leaves or bird droppings.
When attacked, some animals have some security in possessing either the defensive armour of a hard shell or the offensive weaponry of sharp-needled spines, toxic chemicals or poisonous venom.
And there is security of a more desperate kind in autotomy (self-amputation) – eluding a predator’s grasp by discarding a limb or appendage – and thanatosis, the bluff of feigning death as a deterrent to those in pursuit of fresh, live prey.
There is additional security for many in the possession of an entire repertoire of such protective attributes – sufficient to see the South Asian butterfly Chilasa clytia through its entire life cycle. The bird-dropping appearance of the young larva becomes, in the pupa stage, that of a short, snapped-off, dead twig.
When the adult butterfly finally emerges, its wings’ colouring is indistinguishable from that of two other quite different but distasteful species.
The challenge of collecting specimens of the giant frog Limnonectes blythii in the Malayan forest was compounded, reports Dr Shahriza Shahrudin, by its deploying nine separate ‘anti-predator mechanisms’ – including erratic leaping, camouflage (‘its colouring is very similar to leaf litter’) and diving precipitously to the bottom of a pool ‘where it remains motionless for several minutes’.
This prodigious range of admirable, more or less inexplicable, defensive traits and strategies is a continuing source of fascination for biologists.
Take the findings of two recent studies. First, the ancient hagfish, an eel-shaped bottom-dweller, blind and jawless. This opportunist scavenger sniffs out the odour of the dead and dying on the ocean floor, cannibalising them by – bizarrely – tying its long body into a knot that, forced downwards towards its head, provides the leverage for its rasp-like incisors to pinch the flesh off its victims.
The primitive hagfish is, in its turn, vulnerable to being preyed on by others – sharks, conger eels, squid and octopuses. Its ingenious mode of protection involves the secretion of a white, viscid fluid from glands along its body that in contact with seawater expands to form a tenacious ball of slime.
The predating shark, with its gills coated and deprived of oxygen, ‘visibly chokes’, reports Dr Victor Zintzen, who captured the sequence of events on a remote, underwater video camera. ‘Convulsed by a dramatic gagging-type effort to clear the slime, it moves away.’ Meanwhile, ‘the hagfish sustains no injury and continues to feed as before’.
Next, another seemingly simple animal, the unassuming sea cucumber, with a soft cylindrical body like its vegetable namesake, a mouth surrounded by retractable tentacles and the unusual facility of breathing through its anus.
When threatened, it has the further unusual ability to loosen its connective tissue, allowing it to slip through the narrowest of apertures into a hole or crevice before re-expanding so it cannot be extricated. This attribute of mutable connective tissue (as it is known) reaches its apotheosis in one of the most extraordinary coups de théâtres of the natural world.
Cornered by, for example, a hungry crab, the sea cucumber self-eviscerates, dissolving the supportive ligaments of its internal organs before expelling them with powerful muscular contractions through either its mouth or its anus, thus ensnaring the startled crustacean.
This drastic measure surprisingly does the sea cucumber no serious harm as, over the next few days, it reconstitutes its missing organs, in a process only recently described by scientists at Tokyo University’s Centre for Marine Biology.
The process of regeneration, their careful histological studies reveal, takes p place in four stages, initiated by p proliferation of the cells in the gut r rudiments at both ends. These form cavities that t then ‘coalesce with e each other, recreating t the hollow tube of a replacement digestive tract’. In such astonishing ways, l life triumphs over near
c certain death.